curl_sslbackend

type curl_sslbackend = (

  CURLSSLBACKEND_NONE = 0,

  CURLSSLBACKEND_OPENSSL = 1,

  CURLSSLBACKEND_GNUTLS = 2,

  CURLSSLBACKEND_NSS = 3,

  CURLSSLBACKEND_OBSOLETE4 = 4,

  CURLSSLBACKEND_GSKIT = 5,

  CURLSSLBACKEND_POLARSSL = 6,

  CURLSSLBACKEND_WOLFSSL = 7,

  CURLSSLBACKEND_SCHANNEL = 8,

  CURLSSLBACKEND_DARWINSSL = 9,

  CURLSSLBACKEND_AXTLS = 10,

  CURLSSLBACKEND_MBEDTLS = 11

);